Faster (to code) if statements are much faster to read, debug, and modify than naively written if statements. What makes them so great?
explicit conditions
the if tree is “lean” and not “bushy”
A defensive else clause
Refactoring a slow if statement
Consider this (slow to code) if statement:
if foo: if bar < 4: if baz in ["a", "b", "k", "r"]: if qux: x = 0 else: x = 1 else: x = 2 else: x = 3 else: x = 4
When is x = 2? Uh, well definitely when foo is true. Maybe when bar < 4? Not sure. So, um, if we look up from x = 2, it looks like “if baz in…” is lined up with it. So it’s when that’s not true. And before if baz…, both if foo and if bar < 4 are true, so… maybe x = 2 when
foo and bar < 4 and baz not in [“a”, “b”, “k”, “r”]
We’re right. But. Ew.
Avoid Bushy Decision Trees
Kernighan and Plauger agree. In The Elements of Programming Style, they have a rule: “avoid bushy decision trees”…